1. Field of the Invention
The present invention relates to a signal detection circuit and a signal detection method for detecting an electric signal that is output by a photosensor and an electric signal that indicates an on/off state of a mechanical switch, wherein the photosensor has: a light-emitting device; and a light-receiving device that outputs an electric signal corresponding to an amount of light received from this light-emitting device, and the mechanical switch is switchable between on and off states. The present invention also relates to a state detection circuit for detecting a state of the electric signal that is output by the photosensor and the on/off state of the mechanical switch.
2. Description of the Related Art
A photosensor has: a light-emitting device; and a light-receiving device that outputs an electric signal corresponding to an amount of light received from the light-emitting device. The photosensor typically has three terminals. For example, when the light-emitting device is a photodiode and the light-receiving device is a phototransistor, an anode of the photodiode and an emitter of the phototransistor are connected to each other to constitute a power supply terminal of the photosensor. Further, a collector of the phototransistor from which the electric signal corresponding to the amount of light received from the photodiode constitutes a signal output terminal of the photosensor. Still further, a cathode of the photodiode acts as a terminal for connecting a photocurrent limiting resistor for adjusting a current flowing through the photodiode.
For example, as set forth in Japanese Unexamined Patent Publication No. 9-008732, the photosensor, which can output an electric signal corresponding to the amount of light that is received by a light-receiving device from the light-emitting device, is used in various fields.
Further, as set forth in Japanese Unexamined Patent Publication No. 2002-057776, a mechanical switch that is switchable between on and off states is similarly used in various fields.
When a photosensor is used, a dedicated signal detection circuit is needed for detecting the electric signal output by the photosensor. On the other hand, when a mechanical switch is used, another dedicated signal detection circuit is needed for detecting the electric signal output by the mechanical switch. Therefore, when the photosensor and the mechanical switch coexist with each other, respective dedicated signal detection circuits are needed, which results in an increase in the number of parts and an increase in price. In particular, in the case of a miniature electrical apparatus, it is often difficult to build respective dedicated signal detection circuits for the photosensor and mechanical switch therein due to limitations of space.
In view of the above problem, it is an object of the present invention to provide a signal detection circuit and a signal detection method in which one identical circuit can detect an electric signal output by a photosensor and an electric signal indicating an on/off state of a mechanical switch that is switchable between on and off states, and a state detection circuit in which one identical circuit can detect both a state of the electric signal output by the photosensor and the on/off state of the mechanical switch.